Cold cathode electron emitters are known in the prior art and generally comprise an electron emission structure that is spaced apart from a target. A potential is applied between the electron emission structure and the target which is sufficient to cause electron migration from the electron emission structure to the target. Successful cold cathode electron emitters are required to exhibit a low surface work function so as to avoid the necessity of excessively high applied voltages. Surface work function is the energy required to remove electrons from the surface of a material. Hot cathode electron emitters overcome an electron emission structure's surface work function by applying high levels of heat to provide the energy required to stimulate the electron emission.
In general, an electron emission structure is configured with a sharp tip so that the electric field present thereat is highly intense and thus able to overcome the emitter's surface work function. The electric field at a sharp tip is inversely proportional to the radius of the tip, thus a small applied voltage and a very small radius tip (approximately 1-10 manometers) provides a very strong electric field which enables the emission of electrons by the field emission mechanism.
Cold cathode electron emitters have been fabricated using thin-film techniques. Spindt et al. in "Physical Properties of Thin-film Field Emission Cathodes with Molybdenum Cones", Journal of Applied Physics, Volume 47, No. 12, December 1976, pages 5248-5263, describe a field emission cathode which utilizes a molybdenum emitter. Spindt et al. produce such emitters, using micro-lithography techniques, in arrays of molybdenum cones and have demonstrated the availability of currents in the range of 50-150 microamperes per cone.
Kumar et al. in "Diamond-based Field Emission Flat Panel Displays", Solid State Technology, May 1995, pages 71-74, describe a display structure which employs a cold cathode electron emitter. The emission substrate is a dense, nano-crystalline carbon film, with a large percentage of the available carbon exhibiting sp.sup.3 "diamond"-bonded carbon while the remaining material is in the form of sp.sup.2 graphitic carbon. Further details of other field emission displays can be found in "Europe's FPD Development Offers a Chance to Compete", Dance, B., Semiconductor International, July 1995, pages 229-232.
One of the major technical obstacles to the commercialization of field emission displays involves the reliability of the cold cathode electron emission arrays. The lack of reliability originates from the high fields required for emission at room temperature. Over time, these fields (through sputtering or sputtering contamination) damage the sharp emitter tips and thus decrease their electron emission efficiency. For this reason diamond-coated tips have been proposed as cold cathode electron emission structures because diamond, simultaneously provides both mechanical strength and relatively low field operation. Prototypes employing such diamond emitters, however, still suffer from high turn-on voltages, high cost and short working life.
A common feature of many prior art field emission displays is a requirement to switch relatively large voltages on a plurality of address lines. Such switching actions create large voltage excursions which causes noise and other interference affects during the operation of the display. Nevertheless, it has been thought to be a requirement to switch such high voltages, to achieve selective electron emission from the cold cathode emission sources.
Accordingly, it is an object of this invention to provide an improved cold cathode electron emission source which exhibits a lowered surface work function.
It is another object of this invention to provide a method for the manufacture of an improved cold cathode electron emission source which exhibits a lowered surface work function.
It is still another object of this invention to provide an improved cold cathode electron emission source which exhibits an improved electron beam pattern.
It is yet another object of this invention to provide a cold cathode electron emission structure which avoids the need for switching high voltages to achieve display cell activation.